A new study suggests that a mouse virus might play a role in chronic fatigue syndrome, a disease which causes incapacitating exhaustion and malaise.

The study, published in the online edition of the Proceedings of the National Academy of sciences, used blood samples collected from chronic fatigue patients. They also carried out genetic testing on blood samples from eight of the patients.

The researchers found evidence of murine leukemia virus (MLV) in 32 of the 37 patients in the sample group and in seven of the eight from whom they gathered fresh blood samples.

The MIV virus was, however, found only in three of the 44 healthy volunteers who had no history of chronic fatigue syndrome, says the study conducted by a team, comprising researchers from the U.S. FDA, the Brigham & Women's Hospital in Boston and the U.S. National Institutes of Health.

It is estimated that more than one million people in the United States have chronic fatigue syndrome. The symptoms include exhaustion that is made worse by physical activity and alleviated by sleep. The Chronic Fatigue and Immune Dysfunction Syndrome Association of America says people with this disease also experience joint aches and muscle pain, headaches and sore throat.

Last October, another research group had reported in the Science journal about a mouse virus they found in the blood samples of patients suffering from chronic fatigue syndrome. The same team had also reported finding the virus in prostate cancer patients.

After the initial findings, separate research groups tried to establish a link between the virus and fatigue but turned up without any similar association.

However, despite the results of the latest study on the subject, there is still confusion about whether the presence of MLV-related virus gene reflects immune disorders in the human body. We are not sure if this virus alters the immune system and allows other viruses or if it is the MLV that makes people sick.

Another factor that requires an explanation relates to why healthy people also contact MLV-related virus but do not depict any other illness due to it.